body .box {
  width: 400px;
  height: 400px;
  border: solid 1px #ddd;
  margin: 200px auto;
  box-sizing: border-box;
  position: relative;
}
body .box .small-box {
  width: 100px;
  height: 100px;
  border: solid 1px #ddd;
  box-sizing: border-box;
  position: absolute;
  display: flex;
  justify-content: center;
  align-items: center;
}
body .box .small-box:nth-child(1) {
  top: 25%;
  left: 25%;
}
body .box .small-box:nth-child(2) {
  top: 25%;
  left: 50%;
}
body .box .small-box:nth-child(3) {
  top: 50%;
  left: 25%;
}
body .box .small-box:nth-child(4) {
  top: 50%;
  left: 50%;
}
